1. Technical Field
The present disclosure relates to a DC-DC converter control circuit to control a DC-DC converter to moderate fluctuation in an output voltage of the DC-DC converter, and a DC-DC converter including the DC-DC converter control circuit.
2. Description of the Related Art
At present, as mobile devices have become more sophisticated and more compact, switching power supplies using hysteresis control that operates at high frequency, which is efficient and can be made compact, is widely used.
For example, a DC-DC converter that operates while generating a constant output voltage is known, as illustrated in FIG. 1. FIG. 1 is a block diagram illustrating a configuration of a conventional DC-DC converter 10X. In FIG. 1, the DC-DC converter includes a switch SW101, a diode D101, an inductor L101, capacitors C101 and C102, resistors R101 through R105, a buffer amplifier AMP101, a comparator CMP101, and a reference voltage source Vref. When an input voltage Vin is applied to an input terminal (switch SW 101), the DC-DC converter generates an output voltage Vout to a load 101.
The DC-DC converter 10X shown in FIG. 1 generates a ramp signal using a low-pass filter 107 connected to an input voltage Vin side of the inductor L101 and adds the ramp signal to a feedback voltage via the buffer circuit (amplifier) AMP101 to control hysteresis.
In general, in DC-DC converters, an inductor current flowing through the inductor includes a ripple component. It is preferable that the ripple component be within a range of from 10% to 20% of the inductor current (e.g., 100 mA). However, in the DC-DC converter 10X shown in FIG. 1, as the voltage at the input side of the inductor L101 is proportional to the input voltage Vin, the operating frequency fluctuates greatly. Therefore, the ripple component of the output voltage Vout also fluctuates greatly.
In addition, the DC-DC converter shown in FIG. 1 needs the buffer circuit AMP101 to obtain a gain 1. Therefore, the operating frequency of the DC-DC converter 10X depends on characteristics of the buffer circuit AMP101 and the buffer circuit needs to carry out phase compensation. Therefore, essentially the operating frequency cannot be increased a lot.
Thus, the output voltage of the DC-DC converter is affected by the fluctuation in the strength of the ripple component of the inductor current. Therefore, in the DC-DC converter, in order to reduce the fluctuation in the output voltage of the DC-DC converter, it is necessary to keep the strength of the ripple component of the inductor current constant.
In addition, the output voltage of the DC-DC converter is also affected by the fluctuation in the frequency of the ripple component of the inductor current. Therefore, in the DC-DC converter, in order to reduce the fluctuation in the output voltage of the DC-DC converter, it is necessary to keep the frequency of the ripple component of the inductor current Constant as well.